I have been working through the ASF's "Recipes" for the creation of a DSM from Sentinel 1 (A and B) imagery.

I am able to produce a DSM, and am relatively happy with the results in terms of the surface produced - it appears to follow the trends of my known datasets (hills where there should be hills and valleys where there are valleys).

I am however seeing discrepancies between my derived surface and a known point (derived from LiDAR). I generated a DSM using imagery acquired in the same month (a few days either side to improve the Baseline and remove temporal discrepancies) as when my LiDAR dataset was acquired.

I am not going to dispute that the LiDAR Elevation is going to give me a better Z-Value than a Satellite derived DSM. I am however looking to use Sentinel in areas where there is not a decent surface or topographic dataset I can use.

I would like to understand why there is a difference (consistently around 120m) between my DSM and LiDAR surfaces.

How can I improve the vertical accuracy of my DSM? Is the issue a vertical datum issue or perhaps a setting / attribute I should be looking for in the acquisition of the imagery?

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    My first guess would be that one has height-above-ellipsoid and the other is geoid (gravity)-based but 120 m is a lot. Where is the area of interest? Or you might find an online geoid calculator for EGM2008 or EGM96 to check. – mkennedy Oct 24 '18 at 0:34
  • The areas are located in all parts of the globe, so I guess a blanket approach won't work. The area in question here is Central Western Australia. – Keagan Allan Oct 24 '18 at 0:50
  • I checked a point using this geoid calculator and the difference was less than 10 m so something's going on with one or both datasets. – mkennedy Oct 24 '18 at 17:00
  • I found the site using the links provided and the LiDAR was 301, my DSM is 401ish and the geoid calculator told me that at my point on all three datums it is -23.7m ... I am not sure how to interpret that...only that I need to add 23.7 to my DSM to get the pixel to the correct mamsl? which still places my image over 130m above the LiDAR surface. – Keagan Allan Oct 25 '18 at 0:04

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